The invention relates to a catalyst for hydrorefining fraction oils and its preparation process as well as a carrier of the catalyst and its preparation process. More particularly, this invention relates to a catalyst for hydrorefining fraction oils, which comprises metal(s) and/or metal oxide(s) of Group VIB and metal(s) and/or metal oxide(s) of Group VIII, and its preparation process as well a carrier of the catalyst and its preparation process.
In recent years, the quality of crude oil resources is showing a tendency to deteriorate steadily worldwide; the content of sulfur, nitrogen and aromatics in the oils is also increasing obviously. The conflict between the ever-stringent environment regulations and this critical reality becomes intensified day by day. It is well known that hydrogenation process is one of the most efficient means for improving quality of the oils, in which hydrotreating catalyst is the most significant key technology. Therefore, many leading companies have already devoted themselves to improving the existing hydrotreating catalysts and continuously developing hydrotreating catalysts having better properties. The current trend in developing hydrotreating catalyst is focused on further reducing the metal content in the catalyst, increasing its catalytic activity and modifying the properties of carrier to render it more suitable for hydrotreating the inferior-quality oils.
Hydrotreating catalysts generally comprise metals and/or metal oxides having hydrogenation function as components and a catalyst carrier, some of the catalysts may contain additives also.
The mostly used metal and/or metal oxide possessing hydrogenation function is selected from metals and met al oxides of Group VIB and metals and/or metal oxides of Group VIII of the Periodic Table of Elements. Said metal and/or metal oxide of Group VIII can be one or more selected from the group consisting of the metals and/or metal oxides of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, of which nickel and cobalt are mostly selected. Said metal and/or metal oxide of Group VIB can be one or more selected from the group consisting of the metals and/or metal oxides of chromium, molybdenum and tungsten, of which molybdenum and tungsten are mostly selected.
The mostly used additive is one or more selected from the group consisting of the oxides of magnesium, oxides of phosphorus and fluorine.
The mostly used catalyst carriers are those made of silica, alumina and silica-alumina, of which alumina is the most extensively applied catalyst carrier.
In U.S. Pat. No. 3,779,903, a carrier having pore volume of 0.15-0.45 ml/g is prepared via drying and calcining an alumina sol, from which a catalyst comprising 10-18 wt % nickel oxide, 25-40 wt % tungsten oxide and 1-9 wt % fluorine is obtained after the steps of impregnating the carrier with a solution of tungsten and nickel, drying and calcining. However, the catalyst has a high metal content, especially a very high the nickel content, hence resulting in a very high cost of the catalyst.
In U.S. Pat. No. 4,330,395 a catalyst for hydrorefining fraction oils is prepared by taking tungsten compound and aluminum compound as row materials, through drying, calcining and impregnating the carrier with a solution of nickel compound, and thereafter, sulfurizing and fluorinating the catalyst with sulfur compound and fluorine compound, respectively. This catalyst also has the same drawback of overhigh metal content, besides, the preparation process of the catalyst is relatively complex.
In CN 85,104,438B, a hydrorefining catalyst comprising 1-5 wt % nickel oxide, 12-35 wt % tungsten oxide and 1-9 wt % fluorine is manufactured by taking high-purity boehmite as precursor of the catalyst carrier, which is prepared through hydrolysis reaction of alkoxyl aluminium or alkyl aluminium. Although the catalyst has lower metal content and is one of the most active hydrorefining catalysts for fraction oils in the prior art, the cost of the catalyst is still relatively high because the precursor of the catalyst carrier is made of the expensive boehmite.
CN 1,169,336A discloses a catalyst for hydrorefining fraction oils and its preparation process. The catalyst consists of 1-5 wt % nickel oxide, 12-35 wt % tungsten oxide, 1-9 wt % fluorine and alumina as the remainder. Said alumina was prepared by compounding one or more microporous alumina(s) with one or more macroporous alumina(s) in the weight ratio of 75:25-50:50. In said microporous alumina, the volume of pores having a diameter of less than 80 angstrom accounts for more than 95% of the total pore volume; in said macroporous alumina, the volume of pores having a diameter of 60-600 angstrom accounts for more than 70% of the total pore volume. The preparation process of the catalyst comprises, forming and calcining the alumina precursor; then impregnating the material obtained in the previous steps sequentially with a fluorine-containing aqueous solution and a nickel-tungsten containing precursors aqueous solution; drying and calcining after each impregnation step. Said alumina precursor is a mixture of the precursors of said microporous alumina and said macroporous alumina. In this mixture, the ratio of said microporous alumina precursor to said macroporous alumina precursor is so set that the weight ratio of said microporous alumina to said macroporous alumina in the final catalyst product falls in the range of 75:25-50:50. In the alumina carrier of the catalyst as prepared by this process, the volume of pores having a diameter ranging from 40-100 angstrom accounts for higher than 75% of the total pore volume and the catalyst is one of the most active hydrotreating catalysts for fraction oils in the prior art, but the preparation process of the catalyst is rather complex due to the use of two kinds of alumina.
In addition, CN 1,105,053A discloses a catalyst suitable for hydrorefining heavy fraction oils. Said catalyst comprises 1-5 wt % nickel oxide, 15-38 wt % tungsten oxide and 1-9 wt % fluorine as well as a carrier of modified alumina that is obtained by high-temperature treatment in the present of air and steam. The pore distribution of the modified alumina is concentrated in the range of 60-200 angstrom. However, obviously the process has shortcomings in its complicated preparation technology and high energy-consumption as a result of the adoption of high-temperature treatment with air and steam.
As a carrier of hydrogenation catalyst, the differences in pore structure, acidity and preparation method of the alumina manifest a great influence on the catalytic performance. Therefore, many preparation methods have been developed in the prior art in order to meet the requirements of different catalysts for the properties of the carriers.
Take xcex3-Al2O3 for example, pseudo-boehmite via calcination forms xcex3-Al2O3 which is a mostly used carrier or substrate of catalysts. The properties of xcex3-Al2O3 play a very important role in the comprehensive performance of the catalyst when it is used as the carrier or substrate of the catalyst. In general, it is desired that the pseudo-boehmite should have a relatively high crystallinity. The content of bayerite as impurity shall be at very low level, preferable nonexistent. In addition, the content of ion impurities shall be at low level also, the acid radical ions in the alumina product, such as the sulfuric acid radical ions shall not be higher than 2 wt % and alkali metal oxides not higher than 0.15 wt %. The xcex3-Al2O3 carrier formed by calcination of pseudo-boehmite shall possess relatively larger specific surface area, higher strength and proper pore volume as well as narrow pore distribution.
In the prior art, a conventional process for preparing pseudo-boehmite and xcex3-Al2O3 is known as sodium meta-aluminate (or sodium aluminate)-aluminium sulfate (aluminium nitrate, aluminium muriate, nitric acid, or sulfuric acid) process.
U.S. Pat. No. 2,980,632 discloses a process for preparing an alumina-based catalyst, comprising precipitating the hydrated alumina out of the aqueous solution of aluminium compound at pH value of 7-9.5, and aging the slurry for at least 0.25-0.5 hour at higher pH value (10-11). Said hydrated alumina precipitate is obtained by the neutralization reaction between a sodium aluminate solution and an aluminium sulfate solution. Said higher pH value is adjusted by reducing the dosage of said aluminium sulfate solution. In this process for preparing pseudo-boehmite, the amounts of aluminium sulfate is relatively increased because the adjustment of pH value is realized by reducing the dosage of aluminium sulfate. When the pH value rising over 10, self-hydrolysis reaction of sodium aluminate is liable to occur, and as a result, bayerite is formed. Thus on the one hand, said bayerite will cover the surface of the original precipitate, and block up the pores and thereby reducing the pore volume of resultant alumina, and on the other hand, excessive xcex7-Al2O3 will be formed in the resultant alumina. Therefore, it should be well appreciated that the alumina prepared by this process is not suitable for being used as the carrier of the catalyst for hydrorefining fraction oils.
U.S. Pat. No. 4,371,513 discloses a process suitable for preparing spheroidal alumina particles, comprising precipitating alumina under the conditions of specially controlled reactant concentration, reaction temperature, time and pH value, and filtrating at higher pH value. Specifically, this process comprises adding a sufficient portion of the aluminium sulfate solution having an alumina concentration of 5-9 wt % and a temperature of 130-160xc2x0 F. into the water having temperature of 140-170xc2x0 F.; and adjusting pH value of this mixture to 2-5; adding a sodium meta-aluminate solution having an alumina concentration of 18-22 wt % and a temperature of 130-160xc2x0 F. and another portion of said aluminium sulfate solution simultaneously into said mixture so as to precipitate the alumina and form an alumina slurry which is maintained at a pH value of 7-8 and temperature of 140-180xc2x0 F., wherein the feeding velocity of the solutions is controlled in such a way as to effect the formation of boehmite and boehmite as intermediates; adjusting the pH value of the slurry to 9.5-10.5; filtrating the slurry and washing the filter cake to obtain the substantially pure aluminium hydroxide. The pore distribution of the alumina so prepared falls in a wider range (with pore diameters ranging from 100-1000 angstrom). It would be well appreciated that alumina without narrow pore distribution is not suitable for use as carrier of the catalyst for hydrorefining fraction oils.
U.S. Pat. No. 4,248,852 discloses a process for preparing all alumina for use as catalyst carrier. The process comprises cultivating a seed aluminium hydroxide gel having a pH value of 5-6 at a temperature of at least 50xc2x0 C.; sequentially adding (a) an aluminium compound and adjusting the pH value of said sol to reach pH value of lower than 5 or higher than 11 aimed at dissolving the crystals of aluminium hydroxide; adding (b) a neutralizer to adjust the pH value falling back to 6-10 for purpose of facilitating growth of the hydrated alumina; repeating the addition of said aluminium compound and said neutralizer for at least two times in order to make the crystals of said hydrated alumina grow continuously; and drying and calcining the crystals of said hydrated alumina. The alumina prepared by this process possesses relatively larger specific surface area and a pore volume controlled in a certain range (0.5-2 ml/g). The pore distribution of the alumina is narrowed in the range of 0-200 or 100-500 angstrom. However, this process is not preferred because the process adjusts the pH value in large amplitude for at least three times, and as a result, makes the preparation procedure too complex.
GB 2,146,633A discloses a process for preparing an alumina for use as catalyst carrier, comprising (1) adding an aluminium sulfate solution and a sodium aluminate solution simultaneously at a pH value of 6.0-8.5 and temperature of 50-56xc2x0 C. into a deionized water to prepare an aqueous slurry containing amorphous hydrated alumina; (2) adding a sodium aluminate solution into said slurry formed in the first step in an amount sufficient to neutralize said slurry so as to obtain the second aqueous slurry containing at least 7 wt % alumina, wherein the total amount of sodium aluminate used in step (1) and step (2) is equal to 0.95-1.05 of the equivalent amount of aluminium sulfate used in step (I); (3) filtrating the amorphous aluminium hydroxide out of said second aqueous slurry and washing the filter cake sequentially with aqueous ammonia solution, nitric acid solution and aqueous ammonia solution to ensure the final pH value of the filter cake reaching 7.5-10.5; (4) dewatering the filter cake in a filter press to increase the alumina content to 28-35 wt %; kneading the dewatered filter press cake for at least 10 seconds to obtain a doughy material; (5) extruding the doughy material into strips; drying and calcining the extrudate. However, the catalyst using the carrier made of the alumina prepared by this process shows very low activity. In addition, three times of washing the filter cake with aqueous ammonia solution and nitric acid solution render this process rather complicated to operate, and too much waste water to be discharged into the environment.
Petroleum Refining, on pages 11-42, and 50-57, 1978 edition, discloses an aluminium sulfate-sodium meta-aluminate process for preparing xcex3-Al2O3, comprising adding an aluminium sulfate and sodium meta-aluminate with pure water in a certain ratio in co-current flow into a neutralization tank with a stirrer to carry out precipitation reaction at pH value of 7.5-9.0, temperature of 40-70xc2x0 C. and residence time of 15 minutes; collecting the slurry formed in the precipitation process in an aging tank for 30 minutes; maintaining the temperature at a certain degree; aging for 30 minutes and filtrating; then adding pure water in an amount of 30 times (by weight) the dosage of alumina stock into the filter cake for first washing; adding a given amount of sodium carbonate in the initial phase of the washing to adjust pH value of the slurry to 10.0; washing with stirring for 20 minutes and filtrating; repeating washing for three times without adding sodium carbonate; drying at 110-120xc2x0 C. and calcining at 550xc2x0 C. for 4 hours, and finally obtaining the xcex3-Al2O3. The key point in this process is to add sodium carbonate to adjust pH value to 10 in the first washing step. The addition of sodium carbonate fulfills two functions, i.e., increasing pore volume and reducing content of sulfuric acid radical in alumina. However, in view of industrial application, adding sodium carbonate in washing process has following disadvantages: (1) Due to the limit in performance of the industrial filtrating equipment, penetration and leakage phenomena in the filter always occur in company with the filtration process. For this reason, the content of alumina in the cake collected in the first washing step is usually lower than the dosage of alumina fed in the precipitation process. Besides, in the commercial production many sets of filtrating equipment are used simultaneously and there exists a difference in the filtrating performance, so the amounts of alumina collected in different lots might be different. As the required dosage of sodium carbonate depends on the amount of aluminium material fed in the precipitation process, thus making it difficult to determine the dosage of sodium carbonate needed in the process. Therefore, estimation method is usually adopted as an option in the commercial application, though this method apparently showed a great deviation from the real value sometimes. Furthermore, the dosage of sodium carbonate has an important effect on the pore volume and pore distribution of the alumina, consequently, the alumina obtained from the above-mentioned process of adding sodium carbonate often lacking reproducibility in its performance. In turn, the hydrogenation catalysts made from this carrier also suffered the unstability in their catalytic properties. (2) In view of continuous industrial production, the belt filter is usually adopted as a best option in the industrial application. Since the washing procedure can be completed in a single run with this equipment, the yield of alumina and production efficiency are raised while the production cost is reduced. However, on the other hand, the addition of sodium carbonate should be effected in the course of washing and a filtrating step is regarded during the course from aging to first washing, this sequence of the operation has greatly limited the utilization of the belt filter in the industry.
Another conventional process for preparing pseudo-boehmite and xcex3Al2O3 is known as sodium meta-aluminate-carbon dioxide process. Since this process can be operated in combination with the practical conditions of the aluminium production plant, by utilizing the sodium meta-aluminate solution or sodium aluminate solution produced from bauxite and waste carbon dioxide gas as feedstocks to prepare alumina, it has been applied extensively in the industry for cost-effectiveness.
In the prior art, the precipitation reaction (or known as neutralization reaction) between sodium meta-aluminate (or sodium aluminate) and carbon dioxide can be carried out in a batch or continuous way. In the precipitation reaction in batch process, carbon dioxide gas is fed into a great volume of sodium meta-aluminate or sodium aluminate solution, and the pH value (end-point pH) of the precipitation reaction is controlled at 9.5, preferably higher than 10. In the precipitation reaction in continuous process, sodium meta-aluminate or sodium aluminate solution and carbon dioxide contact each other at a certain flow rate, respectively, and pH (pH in the course) value of the precipitation reaction is also controlled at 9.5, preferably higher than 10. From the precipitation reaction at such high pH value, pseudo-boehmite (the precursor of xcex3-Al2O3) having high crystallinity can be obtained. But, as its crystalline particles are in solid spheroidal shape and packed closely, smaller pores are formed in the alumina after calcining, and the pore volume of pores having a diameter in the range of 20-60 angstrom accounts for 60% of the total pore volume, thus detrimentally affecting its application in the preparation of catalyst for hydrorefining fraction oils.
For instance, U.S. Pat. No. 3,268,295 discloses a process for preparing a hydrated alumina having a content of crystalline water of 1.4-1.6 mol/mol alumina and an average crystal size of 20-40 angstrom. In the X-ray diffraction pattern of said alumina, the area within the peak at 20=21.8xc2x0 accounts for 40-90% area of the peak corresponding to boehmite. This process comprises (a) reacting sodium aluminate having sodium content of less than 200 g Na2CO3/l with approximately stoichiometric carbon dioxide to prepare an amorphous aluminium hydroxide, which substantially does not contain crystalline hydrated alumina, at temperature of 25-60xc2x0 C., reaction time of 2-20 minutes and pH value of 10-11, thereby said aluminium hydroxide being precipitated substantially through neutralization reaction instead of hydrolysis reaction; (b) separating said precipitate from mother liquid, washing said precipitate and beating up said precipitate and water into slurry again so as to disperse said precipitate, and-maintaining it in an amorphous state; (c) aging the precipitate in the slurry for 5-90 minutes at temperature lower than 100xc2x0 C. and pH value of 8-9 to transform the amorphous aluminium hydroxide into crystalline hydrated alumina.
EP 0,147,167A2 discloses a process for producing alumina gel by neutralizing aluminate in continuous way, comprising (a) feeding a sodium aluminate solution having a given degree of total causticity and a given alumina to causticity ratio into a reactor; (b) keeping said solution inside the reactor at a given temperature; (c) contacting a neutralizer with said solution and reducing the pH value lower to the preset value, wherein said neutralizer is selected from gases which are soluble in said sodium aluminate solution and from liquids which are insoluble in said sodium aluminate solution; (d) continuously removing the formed alumina gel from the reactor, wherein the removing speed is selected based on the causticity, ratio of alumina to causticity, reaction temperature, pH value and residence time so as to have the alumina gel transform into a particular morphology. It is pointed out on page 7 in this application that the pH value in the neutralization reaction can be in the range from 8.5 to 12 depending on different products as desired. For instance, dawsonite can be produced at pH value of 8.5-10.2 while bayerite can be obtained at pH value of 12, and in case of a pH value in the range of 10.4-10.7, pseudo-boehmite can be mainly obtained.
CN 85,100,161A discloses a process for preparing pseudo-boehmite by utilizing the industrial grade sodium aluminate solution formed in the production of alumina, through the precipitation in carbonation reaction. This process comprises adding distilled water or deionized water into the industrial sodium aluminate solution having an alumina concentration of 70-130 g/l and a temperature of 70-100xc2x0 C. to dilute and cool said industrial sodium aluminate solution until the alumina concentration reaches 20-60 g/l and temperature reaches 15-45xc2x0 C.; removing the Al(OH)3 residue by filtrating said industrial sodium aluminate solution after diluting and cooling; introducing carbon dioxide gas in a concentration of 30-40% to carry out quick precipitation in carbonation reaction in either batch or continuous way, wherein when precipitation in carbonation reaction is carried out in batch way, the carbon dioxide gas is introduced at a flow rate of 2-8 g CO2/g alumina-hr for 10-30 minutes; and when precipitation in carbonation reaction is carried out in continuous way, the carbon dioxide gas is introduced at a flow rate of 1-6 g CO2/g alumina-hr for a carbonation time of 30-90 minutes; heating the slurry after precipitation to 70-100xc2x0 C., holding the temperature constant and aging for 1-6 hours; or directly separating solid from liquid firstly then aging in the washing process; washing the separated solid with distilled water or deionized water at 70-100xc2x0 C. for 1-4 times, wherein a portion of the washing liquid is fed back to dilute said industrial sodium aluminate solution; recycling the separated mother liquid and the remaining washing liquid to the aluminium production flow; finally, drying and grinding the washed wet stock by a conventional method to obtain the pseudo-boehmite powder. According to the precipitation conditions as stated in the application, the end-point pH value or the process pH value in the course of precipitation is also controlled in the range from 10.5 to 12.0.
In the prior art, the reason for controlling the end-point pH or the process pH in the range of 10-12 in the case of producing pseudo-boehmite by sodium meta-aluminate (or sodium aluminate)-carbon dioxide process is that when the end-point pH value or the process pH in the course of reaction is less than 10, particularly less than 9.5, in the precipitation process, aluminium hydroxide and sodium bicarbonate formed in the precipitation process shall react with each other to produce dawsonite (NaAl(OH)2CO3). Taking the production of pseudo-boehmite by sodium meta-aluminate-carbon dioxide process as an example, the following reactions exist in the precipitation process: 
Since dawsonite is not soluble in water, it cannot be removed in the washing step, as a result the sodium content in the product is too high, thereby seriously affecting the product quality.
U.S. Pat. No. 4,500,444 discloses a process for preparing a basic aluminium carbonate, comprising reacting sodium meta-aluminate with carbon dioxide in aqueous solution at pH value of 6.8xc2x10.2 and temperature of 10-50xc2x0 C. to form basic aluminium carbonate colloid, and separating said colloid from reaction medium by filtration. Then pseudo-boehmite can be formed by hydrolyzing said colloid with acid. The contents of sulfuric acid radical and sodium ions in the pseudo-boehmite made by this process are reduced obviously. But the crystallinity, pore volume and pore diameter of the pseudo-boehmite are also very low, therefore the alumina prepared therefrom is not suitable for use as carrier for catalyst for hydrorefining fraction oils. At same time, the washing step becomes very difficult due to peptization of the acid. In addition, this process comprises decomposition of basic aluminum carbonate, so there is a large consumption of expensive organic acid and consequently the productive cost goes up, and more seriously, corrosion caused by the process is detrimental to the productive facilities.
An object of the present invention is to provide a novel catalyst for hydrorefining fraction oil, which possesses higher catalytic activity and the preparation process thereof. Another object of the present invention is to provide an alumina carrier for supporting said catalyst and the preparation process thereof.
Said catalyst according to the present invention comprises an alumina carrier and at least one metal and/or thereof oxide of Group VIB and at least one metal and/or thereof oxide of Group VIII supported on said alumina carrier; the pore volume of said alumina carrier is not less than 0.35 ml/g, in which the pore volume of the pores having a diameter of 40-100 angstrom accounts for more than 80% of the total pore volume, said alumina carrier is prepared by one or two of the following processes, wherein:
Process 1 comprises contacting a solution of sodium meta-aluminate or sodium aluminate with one or more of the solutions of aluminium sulfate, aluminium nitrate, aluminium chloride, nitric acid and sulfuric acid to carry out the primary precipitation reaction that may run in in a continuous way; aging the obtained aluminium hydroxide; separating solid from liquid, and washing, drying and calcining the obtained solid resultant, wherein the pH value of said primary precipitation reaction is 6-9.5, the temperature of said primary precipitation is 10-100xc2x0 C., the slurry formed in said precipitation reaction (primary precipitation) is collected in a secondary precipitation tank for a collecting time of not less than 10 minutes, and after finishing the collection, the slurry is switched to another secondary precipitation tank to continue the collection; to the secondary precipitation tank where the collection is finished, adding one or more of alkali carbonate, a mixed solution of alkali bicarbonate and aqueous ammonia, ammonium carbonate and ammonium bicarbonate in order to carry out the secondary precipitation reaction, wherein the pH value of the secondary precipitation reaction is controlled at 9.0-10.5.
Wherein concentration of said aluminium meta-aluminate or sodium aluminate solution as well as the concentration of aluminum sulfate, aluminium nitrate, aluminium chloride, nitric acid and sulfuric acid solution can be any, or possibly existing concentration, provided that the pH value of 6-9.5 of the primary precipitation reaction is guaranteed. In order to prepare pseudo-boehmite efficiently, the concentration of sodium metal-aluminate or sodium aluminate solution is preferably 30-300 g alumina/l, the concentration of aluminum sulfate, aluminium nitrate and aluminium chloride is preferably 10-120 g alumina/l, the concentration of nitric acid and sulfuric acid is preferably 5-15 wt %.
The addition of the substances such as sodium carbonate, ammonium carbonate and ammonium bicarbonate can be carried out in solid form or aqueous solution form, preferably aqueous solution form.
The pH value of said primary precipitation reaction is preferably 6-9. The temperature of said primary precipitation reaction is preferably 30-90xc2x0 C. The collecting time is preferably 10-90 minutes. The pH value of secondary precipitation is preferably 9.5-10.5.
The method for separating solid from liquid, can adopt conventional methods, such as filtration method or centrifugal separation method.
Said aging can be carried out under conventional conditions; normally the temperature of said aging is in the range of 5-100xc2x0 C., preferably 30-100xc2x0 C., more preferably 30-90xc2x0 C.; the time of said aging is longer than 0.5 hour, preferably 1-8 hours.
Said washing can be carried out by conventional method; the object of said washing is to remove the impurity ions from the resultant alumina, such as sulfate ion, sodium ion, etc.; said washing shall ensure the content of alkali metal oxides in the resultant alumina to be less than 0.15 wt %, and the content of sulfate ion less than 2 wt %.
When preparing alumina carrier, there may be and preferably there is a shaping step prior to drying. The shaping method can adopt the various existing methods, such as tabletting method, spheroidal forming method and extrusion forming method etc.; preferably the extrusion forming method. Various existing peptizers and/or extrusion aids can be added in the shaping process, said peptizers can be selected from the group consisting of various inorganic acids or organic acids, such as chlorhydric acid, nitric acid, citric acid and acetic acid. Said extrusion aids can be selected from starch substances, cellulose substances and the like.
Said drying condition is conventional drying condition, the drying temperature can be in the range from ambient temperature to the temperature lower than the crystal transformation temperature of pseudo-boehmite, preferably 100-200xc2x0 C.
Said calcining condition is conventional calcining condition, the calcining temperature is normally 500-900xc2x0 C., preferably 550-850xc2x0 C.; the calcining time is normally 2-8 hours, preferably 3-6 hours.
Process 2 comprises contacting a solution of sodium meta-aluminate or sodium aluminate with a gas containing carbon dioxide to carry out precipitation in batch or continuous way; aging the obtained aluminium hydroxide; separating solid from liquid; washing, drying and calcining the obtained solid resultant, wherein the end-point pH value or process pH value in the course of said precipitation is controlled in the range of 6-9.5, the time of said precipitation reaction or the residence time is less than 40 minutes, the temperature of said precipitation reaction is 10-100xc2x0 C., and as soon as said precipitation reaction is ended a basic substance is added promptly so as to make the pH value of the slurry rise to higher than 9.5 or quickly carry out the separation of the solid from liquid and washing.
The concentration of said aluminium meta-aluminate or sodium aluminate solution can be any, or possibly existing concentration. In order to prepare pseudo-boehmite efficiently, the concentration of said sodium meta-aluminate or sodium aluminate solution is preferably 5-200 g alumina /l, more preferably 5-120 g alumina/l.
Said gas containing carbon dioxide can be pure carbon dioxide gas or a mixed gas consisting of carbon dioxide and inert gas which does not affect the reaction, such as a mixture of carbon dioxide and one or more matters selected from the group consisting of air, nitrogen, helium and argon, etc. The carbon dioxide content in said gas containing carbon dioxide can vary in a wide range, and normally the carbon dioxide content is not less than 5 v %, preferably not less than 20 v %.
Said precipitation can be carried out in a batch way. When adopting this way, the procedures comprise adding said sodium meta-aluminate or sodium aluminate solution in a precipitation tank firstly; introducing said gas containing carbon, dioxide through the bottom of the tank; controlling the reaction temperature at 10-100xc2x0 C., preferably 10-80xc2x0 C.; and controlling the end-point pH value at 6-9.5, preferably 6.5-9.3; adjusting the concentration and dosage of said sodium meta-aluminate or sodium aluminate solution as well as the concentration and flow rate of said gas containing carbon dioxide to make sure the time of said precipitation reaction not to exceed 40 minutes, preferably not to exceed 30 minutes; adding basic substance to make the pH value of the slurry rapidly rise to higher than 9.5, preferably 9.5-11.5, as soon as said precipitation reaction is ended; or quickly carrying out the separation of the solid from liquid, and washing; thereafter aging, filtrating, washing and drying under conventional conditions, to obtain pseudo-boehmite, which is then calcined and formed to obtain the alumina carrier.
Said precipitation reaction can be carried out in a continuous way. When adopting this way of precipitation, the procedures comprise adding deionized water into a precipitation tank in advance; introducing said gas containing carbon dioxide through the bottom of the tank and simultaneously feeding the sodium meta-aluminate or sodium aluminate solution through the top of the tank to make said sodium meta-aluminate or sodium aluminate solution to contact said gas containing carbon dioxide in countercurrent flow; controlling the temperature of said precipitation reaction in the range of 10-100xc2x0 C., preferably 10-80xc2x0 C.; controlling the concentration and the flow rate of said sodium meta-aluminate or sodium aluminate solution as well as the concentration and the flow rate of said gas containing carbon dioxide to make the process pH in the course of the precipitation reaction reach 6-9.5, preferably 6.5-9.3, and make the residence time not to exceed 40 minutes, preferably not to exceed 30 minutes; collecting the slurry formed in said precipitation reaction in batch or continuous way in an aging tank, and adding basic substance in batch or continuous way to make the pH value of said slurry rise to higher than 9.5, preferably in the range of 9.5-11.5, switching said slurry formed in said precipitation reaction to another aging tank after collecting for a given time; aging said slurry having pH of higher than 9.5 in the first aging tank; filtrating, washing and drying to get pseudo-boehmite and calcining to obtain alumina carrier.
Said basic substance is one or more matters selected from the group consisting of inorganic bases, organic bases and their aqueous solutions, wherein said inorganic base is one or more matters selected from the group consisting of hydroxides, meta-aluminates, carbonates and bicarbonates of alkali metal, ammonium carbonate, aqueous ammonia and their aqueous solutions. Said organic base is one or more matters selected from the group consisting of water soluble amines, carbamide, pyridine and their aqueous solutions, preferably one or more matters selected from the group consisting of water soluble aliphatic amines, hydroxy-ammonium hydroxide, urea, pyridine and their aqueous solutions, more preferably one or more matters selected from the group consisting of methylamine, ethylamine, propylamine, propane diamine, isomers of butyl amine, isomers of pentyl amine, tetraethylammonium hydroxide, urea, pyridine and their aqueous solutions.
Said method for separating solid from liquid can adopt either filtration method or centrifugal separation method. The rapid washing after separating solid from liquid is aimed at removing the resultant sodium carbonate, which can form dawsonite. In general, said washing is carried out with deionized water in a volume of not less than 10 times of that of the weight of solid product for at least once.
Said aging can be carried out under conventional aging conditions; the temperature of said aging is normally in the range of 5-100xc2x0 C., preferably 30-100xc2x0 C., more preferably 50-100xc2x0 C.; the time of said aging is longer than 0.5 hour, preferably 1-8 hours. When adjusting the pH value by adding basic substance, mother liquid or deionized water can be used as aging medium; in the case of separating solid from liquid in a quick way, the deionized water is generally selected as the aging medium.
Said washing after aging can be carried out by conventional method; the object of said washing is to remove the impurity ions inside and to ensure the content of alkali metal oxides inside to be less than 0.15 wt %.
Said drying conditions are conventional drying conditions, the drying temperature can be in the range from ambient temperature to temperature lower than the crystal transformation temperature of pseudo-boehmite, preferably 100-200xc2x0 C.
When preparing alumina carrier, similarly, there may be and preferably there is a shaping step prior to drying.
Said calcining conditions are conventional calcining conditions, for example, the calcining temperature is normally in the range of 500-900xc2x0 C., preferably 550-850xc2x0 C.; and the calcining time is normally in the range of 2-8 hours, preferably 3-6 hours.
According to the catalyst provided by the present invention, said metal and/or thereof oxide of Group VIB is one or more selected from the group consisting of chromium, molybdenum, tungsten metals and their oxides, preferably one or more selected from the group consisting of molybdenum, tungsten metals and the oxides thereof, more preferably one or more selected from tungsten metal and the oxides thereof. The content of said metal of Group VIB in the catalyst is 12-35 wt %, calculated in oxide.
According to the catalyst provided by the present invention, said metal and/or thereof oxide of Group VIII is one or more selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum metals and their oxides, preferably one or more selected from the group consisting of cobalt, nickel and their oxides, more preferably nickel and the oxides thereof. The content of said metal of Group VIII in the catalyst is 1-5 wt %, calculated in oxide and based on the total weight of the catalyst.
The catalyst provided by the present invention may and preferably, contain 1-9 wt % fluorine based on the total weight of the catalyst.
The process for preparing the catalyst provided by the present invention comprises impregnating the catalyst carrier with aqueous solution containing metals of Group VIB and Group VIII, thereafter drying and calcining, wherein said catalyst carrier is the alumina carrier prepared by process 1 or process 2.
Said aqueous solution containing metal of Group VIB and Group VIII is aqueous solution containing metal compounds of Group VIB and Group VIII, preferably the aqueous solution contains molybdenum and/or tungsten and nickel and/or cobalt compound, such as a mixed aqueous solutions containing one or more selected from the group consisting of ammonium metawolframate, ammonium wolframate, ethyl-anmmonium metawolframate and ammonium molybdate, and containing one or more selected from the group consisting of nickel, metawolframate, nickel nitrate, nickel acetate cobalt nitrate, cobalt acetate; more preferably the aqueous solution contains tungsten and nickel compound, such as a mixed aqueous solutions containing one or more selected from the group consisting of ammonium metawolframate, ammonium wolframate and ethyl-metawolframate, and containing one or more selected from the group consisting of nickel metawolframate, nickel nitrate and nickel acetate.
Wherein, before impregnating the catalyst carrier with said aqueous solution containing said metals of Group VIB and VIII, there may be and preferably conclude steps of impregnating the catalyst carrier with aqueous solution containing fluorine, drying and calcining. Said aqueous solution containing fluorine is aqueous solution containing inorganic compound of fluorine, for example, the aqueous solution of ammonium fluoride and/or hydrogen fluoride.
The drying after impregnating the catalyst carrier with the aqueous solution containing said metals of Group VIB and Group VIII or after impregnating the catalyst carrier with the aqueous solution containing fluorine is carried out under respectively conventional drying condition; the drying temperature can be in the range from ambient temperature to 300xc2x0 C., preferably 100-200xc2x0 C.
The calcination temperature after impregnating the catalyst carrier with the aqueous solution containing said metals of Group VIB and Group VIII or after impregnating the catalyst carrier with the aqueous solution containing fluorine is in the range from 400-600xc2x0 C. for the calcination time is 1-8 hours, preferably 2-5 hours.
When preparing alumina carrier by the process 1 according to the present invention, the addition of alkali carbonate, the mixed solution of alkali bicarbonate and aqueous ammonia, ammonium bicarbonate and ammonium carbonate is carried out before aging and filtrating. The amount of sodium carbonate, mixed solution of sodium bicarbonate and aqueous ammonia, ammonium bicarbonate and ammonium carbonate can be accurately added based an the dosage of alumina feedstock, therefore, the shortcoming existing in the method of adding sodium carbonate during washing process in the prior art has been overcome. The pseudo-boehmite, as the precursor of alumina prepared by the process 1 according to the present invention, is inform of fibre, the alumina carrier made from the pseudo-boehmite not only has a pore volume of 0.45-0.75 ml/g, in which the pore volume of pores having a diameter of 40-100 angstrom accounts for more than 80% of the total pore volume, but also possesses good reproducibility. The alumina carrier so prepared shows eminent consistency in its property and reliable stability, hence it is suitable for use as the carrier of the catalyst for hydrorefining fraction oils.
The inventor of the present invention has discovered that during the process of said precipitation reaction between said sodium meta-aluminate or sodium aluminate and carbon dioxide, though the reaction of forming dawsonite may occur in company with the reaction of sodium carbonate and aluminium hydroxide when the end-point pH or process pH in the course of the reaction is lower than 9.5, the formation of dawsonite shall need an enough time to take place, generally speaking, 40 minutes or longer. It seems to imply such a possibility that as long as the pH value of precipitation is lower than 9.5, the pseudo-boehmite which substantially contains no dawsonite still can be obtained if only it is ensured that the time of having pH value at lower than 9.5 does not last long than 40 minutes. However, it is well known that the formed aluminium hydroxide usually need to be aged for an aging time of generally longer than 0.5 hour, besides the time of gel formation, in other words, the time of having the pH lower than 9.5 will be surely longer than 40 minutes. Against the drawback mentioned above, the inventor has ingeniously invented a process as described in Process 2 of the present invention. Process 2 has overcome the drawback originated from the relatively small pore volume and relative small pore diameter in the alumina carrier made from the pseudo-boehmite having crystals in form of solid spheroidal and packed closely prepared according to the prior artxe2x80x94sodium meta-aluminate or sodium aluminate carbon-dioxide process. The pseudo-boehmite prepared by Process 2 is in form of fibre, and the alumina made from the pseudo-boehmite after calcining has a pore volume of 0.45-0.75 ml/g, in which a pore volume of the pores having a diameter in the range of 40-100 angstrom accounts for more than 80% of the total pore volume. The alumina having this property is particularly suitable for use as the carrier of the catalyst for hydrorefining fraction oil.
Because the alumina having special property prepared by the special process mentioned above is adopted, the catalyst according to the present invention possesses the catalytic activity higher than the prior art. For example, the desulfurization-hydrogenation activity, denitrogeneration-hydrogenation activity and aromatic saturation-hydrogenation activity of the catalyst are generally higher than the catalyst disclosed in CN 85104438B. In addition, the catalyst according to the present invention still exhibits relatively high catalytic activity when it is employed in hydrorefining the inferior fraction oils having high sulfur content. For another example, when the catalyst according to the present invention is employed under lower bulk density (packing density) (0.78-0.88 g/ml), its properties of hydrodesulfurization, hydro-denitrogeneration and aromatic saturation are still higher than the corresponding activities of the catalyst (having bulk density of  greater than 1.0 g/ml) disclosed in CN 85104438B, that is to say, the catalyst according to the present invention still possesses higher hydrogenation activity under higher space velocity.
In addition, the catalyst according to the present invention embodies the advantage of low metal content of the catalyst disclosed in CN 85104438B. Furthermore, the alumina carrier prepared by Process 1 and Process 2 has very low cost, which only accounts for 15-50% of the cost of the carrier of CN 85104438B. Therefore, the cost of the catalyst according to the present invention is correspondingly reduced by a big margin. The catalyst provided by the present invention is a catalyst having high activity and low cost, which possesses significant value in the commercial application.
The alumina carrier according to the present invention is not only particularly suitable for use as the carrier of the catalyst for hydrorefining fraction oils but also suitable for use as the carrier or substrate of the catalyst for hydrocracking fraction oils.
The catalyst provided by the present invention is particularly suitable for hydrorefining the petroleum fraction oils having a distillation range of 80-550xc2x0 C. The catalyst provided by the present invention in conjunction with the hydrocracking catalyst can be used for improving the quality of heavy fraction oils by hydrogenation, particularly suitable for improving the quality of heavy fraction oils by hydrogenation under medium-pressure.
The conventional hydrorefining process conditions can be utilized when the catalyst according to the present invention is used for hydrorefining fraction oils, such as reaction temperature of 200-500xc2x0 C., preferably 300-400xc2x0 C., reaction pressure of 2-24 MPa, preferably 3-15 MPa; hourly liquid space velocity of 0.1-30 hrxe2x88x921, preferably 0.2-10 hrxe2x88x921, and volume ratio of hydrogen to oil of 50-5000, preferably 200-1000.